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Biomedical subjects

E Bamberg

Publications and source records attributed to E Bamberg.

At least 109 records · Page 6Linked to original sources
PubMed1981

[The long Q-T syndrome without Q-T prolongation (author's transl)].

Case description of a 30 year-old woman with recurrent attacks of symptomatic ventricular tachyarrhythmias but without Q-T prolongation in the electrocardiogram. All conventional antiarrhythmic agents failed to suppress the arrhythmia and electrical defibrillation had to be carried out 99 times. Blockade of the left stellate ganglion with lidocaine followed by stellectomy led to successful control of the dangerous rhythm disturbance for a follow-up period of 1.5 years. As in patients with the classical long Q-T syndrome stellate ganglion blockade and stellectomy might be indicated in cases with the so called latent Q-T syndrome and life threatening ventricular arrhythmias resistant to antiarrhythmic agents.

Adult↗
PubMed1981

Transmembranous incorporation of photoelectrically active bacteriorhodopsin in planar lipid bilayers.

Various methods to incorporate bacteriorhodopsin in black lipid membranes are reported. Both purple membrane patches and monomeric bacteriorhodopsin were used as starting material. The incorporation of bacteriorhodopsin into planar lipid bilayers was achieved by the following methods. (i) Purple membrane patches were transferred from water to solutions of lipids in n-alkanes. Black membranes were formed from such organic suspensions. (ii) Lipid layers containing solvent and purple membranes were spread on an air/water interface. These layers were used to form planar bilayers. (iii) Vesicles containing purple membranes or monomeric bacteriorhodopsin were spread on an air/water interface and, from the resulting layer, bilayers were formed. On illumination, steady-state photocurrents were observed in all three cases, indicating that these methods lead to functional transmembranous integration of the protein in the planar black lipid membrane. The influence of an applied electric field on the pumping process was studied on membranes formed by using method i. At approximately 200 mV, the photocurrent tends to zero. Furthermore, it was possible to make planar lipid bilayers photoelectrically active by adding vesicles containing monomeric bacteriorhodopsin to the bathing solution. Because, in this case, only transient photocurrents were observed, it can be concluded that the vesicles are attached to but not fused with the black lipid membrane.

Bacteriorhodopsins↗
PubMed1981

Plasma levels of androstenedione, epitestosterone, testosterone and oestrogens in cows at parturition.

The concentration of total unconjugated oestrogens in the peripheral plasma of cows increased from 2.00 +/- 0.20 (S.E.M.) ng/ml 7 days before to 3.87 +/- 0.50 ng/ml 1 day before parturition and declined to values below 0.30 ng/ml on day 2 post partum. The concentrations of androstenedione, epitestosterone and testosterone remained approximately constant at 0.90 +/- 0.10, 0.92 +/- 0.08 and 0.40 +/- 0.20 ng/ml respectively during the last week of pregnancy. After parturition the concentration of the three androgens declined rapidly. Similar to data obtained in goats we did not find a marked increase in androgen levels in the peripheral blood of cows before parturition.

Androstenedione↗
PubMed1981

[Localization of beta-n-acetylhexosaminidase in stallion epididymis (author's transl)].

The localization of beta-N-acetylhexosaminidase activity in 6 different segments of the epididymis was investigated in 8 stallions using biochemical and histochemical methods. The highest enzyme activity was found in segment D while the other segments displayed a much weaker reaction There was no or only low enzyme activity present in the epididymal fluid of the proximal 3 segments, whereas it was high in the distal 3 segments. The biological function of beta-N-acetylhexosaminidase in the epididymis is discussed briefly.

Animals↗
PubMed1980

Effect of immunization of male rabbits against androstenedione.

After active immunization of male rabbits against androstenedione and with increasing antibody titre the concentration of androstenedione and testosterone in peripheral blood increased more than 1000-fold resp. 20-fold above values of control animals. On histological examination of the testes a marked Leydig's cell hyperplasia was found, though there was no difference in testis weight.

Androstenedione↗
PubMed1979

Formation of ionic channels in black lipid membranes by succinic derivatives of gramicidin A.

Different succinyl derivatives of Gramicidin A were synthesized and their activity was investigated with different methods on lipid bilayer membranes. The succinyl derivatives of Gramicidin A can be classified as three different types, the O-succinyl derivative, the N-succinyl derivative and the N-O-succinyl derivative of Gramicidin A. An O-pyromellityl-N-succinyl gramicidin was synthesized which can be attributed to the latter class. It was found that O-succinyl gramicidin behaves like the unmodified Gramicidin A despite a charge effect on single-channel conductance, arising from the negative charge of the succinic residue at the mouth of the channel. The activity of N-succinyl and N-O-succinyl gramacidin and of O-pyromellityl-N-succinyl-gramicidin depends strongly on the pH of the electrolyte solution. It is demonstrated that at low pH (less than or equal to 5) the N-succinyl derivatives show high activity, whereas at high pH (greater than or equal to 7) the activity is sharply reduced or disappears totally. From these experiments it can be concluded that, for the formation of a dimeric gramicidin channel, the hydrogen of the formyl group can be replaced by a protonated carboxylic group of a succinic residue. Further results, obtained by measurement of the single-channel conductance and of the reaction rate constants for the channel formation, are discussed in terms of the structural basis of the single stranded model for the gramicidin channel. On this basis the double stranded helix can be excluded and an interesting head-to-head single stranded beta(pi L.D.) helical channel is described which contains carboxyl groups at the head-to-head junction.

Electric Conductivity↗
PubMed1979

Dicarboxylic acid analogs of gramicidin A: dimerization kinetics and single channel properties.

According to the model of Urry, the cation-permeable gramicidin channel is a dimeric helix formed by association of two peptide monomers linked at their amino ends. In this paper the channel properties of gramicidin analogs are described which have been obtained by chemical modification at the coupling site of the two half-channels. In these analogs the amino terminal -CHO group is replaced by -CO(CH2)nCCOH (n = 2, 3, 4, 5, 6). All analogs form conducting channels in black lipid membranes with the same general properties as found for gramicidin A. The observation that the channel-forming activity decreases with increasing pH is consistent with the notion that the half-channels are linked at the amino terminus. The channel lifetime of the different analogs varies between 2 msec and greater than of equal to 50 sec, the longest lifetime being found for the compound with n = 3. The single-channel conductance : formula : (see text) is always smaller than that of gramicidin A, but the reduction of : formula : (see text) depends on the nature of the permeable ion. Ion specificity was studied at 1 M electrolyte by measuring the conductance : formula : (see text) for different permeable ions (Na+, K+, Cs+). The conductance ration : formula : (see text) (Cs+)/ : formula : (see text) (Na+) was found to vary between 2 and 10.5 for the different analogs.

Chemical Phenomena↗
PubMed1979

Effects of surface charge on the conductance of the gramicidin channel.

The electric conductance of the cation-permeable gramicidin channel in negatively charged phosphatidylserine membranes has been studied. At low electrolyte concentrations the single-channel conductance is much larger in the negatively charged membrane than in a neutral membrane. This enhancement of conductance is in agreement with theoretical expectations, although a complete description of the salt concentration dependence of conductance was not possible. The results of these experiments may be compared with previous studies of a negatively charged gramicidin analog (O-pyromellityl gramicidin). It is found that the electrostatic effect on the conductance is much larger for a neutral channel embedded in a negatively charged lipid than for the negatively charged O-pyromellityl analog (with three charges at the channel mouth) embedded in a neutral lipid.

Electric Conductivity↗